1. Field of the Invention
The present invention relates to a method of performing a double-sided process, and more particularly, to a method of performing a double-sided process, which effectively protects a structural pattern on a front surface of the wafer.
2. Description of the Prior Art
Micro-electromechanical components, for example, pressure sensors or microphones, have more complex mechanically designed structures than conventional semiconductor components, such as hanged membrane structures, and require a double-sided process for manufacturing. The steps of the double-sided process are complex, so the manufacture has many difficulties. The hanged membrane structure of micro-electromechanical components is frail, so rupture occurs easily as the cutting process is performed. Furthermore, the front structure of the wafer can be easily damaged as the back process is performed.
In general, the cutting process of the micro-electromechanical components is performed after the front and back processes are completed, and the cutter cuts the wafer to a plurality of dies. Utilizing the cutter to perform the cutting process has the following problems:
(1) 100 μm is the limit of the cutting width of the cutter. As the size of the components becomes smaller, the integration of the wafer cannot increase as it is affected by the size of the scribe lines;
(2) As the integration of the wafer increases, the cycle time of the cutting process increases to affect yield;
(3) Utilizing the cutter produces many fractures, and the wafer needs to perform a clean process using clean liquid; however, the frail hanged membrane structure fractures more easily during the clean process.
The cutting process of the prior art can also use an etching process as well as the cutter. Please refer to FIGS. 1-3. FIGS. 1-3 are schematic diagrams of a method of a cutting process performed by an etching process according to the prior art. As FIG. 1 shows, a wafer 10 is provided, and a sacrificial layer 12 and a structure layer 14 are formed on the front surface of the wafer 10. Then, a photoresist pattern 16 is formed on the surface of the structure layer 14. The photoresist pattern 16 is a hard mask for an etching process, so as to define front scribe lines 18 on the front surface of the wafer 10.
As FIG. 2 shows, the photoresist pattern 16 is removed, and the wafer 10 is turned over. The structure layer 14 is connected with a carrier wafer 22 by a bonding layer 20. Subsequently, the other photoresist pattern 24 is formed on the back surface of the wafer 10. The photoresist pattern 24 is a hard mask for a dry etching process in order to define back scribe lines 26 and a chamber 28 of micro-electromechanical components. As FIG. 3 shows, the photoresist pattern 24 is removed, and a wet etching process is performed to remove the sacrificial layer 12, so as to form a hanged membrane structure 30.
As the prior art utilizes the wet etching process to remove the sacrificial layer 12, if the material of the bonding layer 20 and that of the sacrificial layer 12 have poor etching selectivity, the etching liquid will corrode the front surface of the structure layer 14 during the etching process, and the hanged membrane structure 30 will be damaged. Utilizing another method, even if the bonding layer 20 is selected to have a better protection ability, the hanged membrane structure 30 will still fracture, because of the stress caused from the bonding layer 20 stacked on itself.